The present invention relates to a laryngeal mask airway device. More specifically, the present invention relates to reduced cost laryngeal masks, improved geometric configurations for laryngeal masks, and to methods of inexpensively fabricating such masks.
The laryngeal mask airway device (LMA) is a well known device that is useful for establishing airways in unconscious patients. LMAs have been in use for about twelve years and offer an alternative to the older, even better known, endotracheal tube. For at least seventy years, endotracheal tubes comprising a long slender tube with an inflatable balloon disposed at the tube's distal end have been used for establishing airways in unconscious patients. In operation, the endotracheal tube's distal end is inserted through the mouth of the patient, past the patient's laryngeal inlet (or glottic opening), and into the patient's trachea. Once so positioned, the balloon is inflated so as to form a seal with the interior lining of the trachea. After this seal is established, positive pressure may be applied to the tube's proximal end to ventilate the patient's lungs. Also, the seal between the balloon and the inner lining of the trachea protects the lungs from aspiration (e.g., the seal prevents material regurgitated from the stomach from being aspirated into the patient's lungs).
Although they have been enormously successful, endotracheal tubes suffer from several major disadvantages. The principal disadvantage of the endotracheal tube relates to the difficulty of properly inserting the tube. Inserting an endotracheal tube into a patient is a procedure that requires a high degree of skill. Also, even for skilled practitioners, insertion of an endotracheal tube is sometimes difficult or not possible. In many instances, the difficulty of inserting endotracheal tubes has tragically led to the death of a patient because it was not possible to establish an airway in the patient with sufficient rapidity.
In addition to this principal disadvantage, there are also other disadvantages associated with endotracheal tubes. For example, intubation with an endotracheal tube often causes patients to suffer from severe “sore throats”. The “sore throat” is principally caused by friction between the tube and the notch between the patient's arytenoid cartilages. Another disadvantage is that patients can not cough effectively while intubated with an endotracheal tube. Yet another problem with endotracheal tubes relates to the manner in which they are inserted. Inserting an endotracheal tube normally requires manipulations of the patient's head and neck and further requires the patient's jaw to be forcibly opened widely. These necessary manipulations make it difficult, or undesirable, to insert an endotracheal tube into a patient who may be suffering from a neck injury. Still another disadvantage is that endotracheal tubes provide an airway that is relatively small or narrow. The size of the airway must be relatively narrow because the distal end of the tube must be sufficiently small to fit into the trachea.
In contrast to the endotracheal tube, it is relatively easy to insert an LMA into a patient and thereby establish an airway. Also, the LMA is a “forgiving” device in that even if it is inserted improperly, it still tends to establish an airway. Accordingly, the LMA is often thought of as a “life saving” device. Also, the LMA may be inserted with only relatively minor manipulations of the patient's head, neck, and jaw. Further, the LMA provides for ventilation of the patient's lungs without requiring contact with the sensitive inner lining of the trachea and the size of the airway established with an LMA is typically significantly larger than the size of the airway established with an endotracheal tube. Also, the LMA does not interfere with coughing to the same extent as endotracheal tubes. Largely due to these advantages, the LMA has enjoyed increasing popularity over the last twelve years.
FIG. 1 shows a perspective view of a prior art LMA 100 and FIG. 2 illustrates an LMA 100 that has been inserted into a patient. LMAs such as LMA 100 are described for example in U.S. Pat. No. 4,509,514. LMA 100 includes a flexible cylindrical tube 110 and a mask portion 130. Tube 110 extends from a proximal end 112 to a distal end 114 and mask portion 130 is coupled to the tube's distal end 114. Mask portion 130 includes a proximal end 132 and a generally elliptical inflatable cuff 134. Mask portion 130 also defines a central passageway extending from proximal end 132 to an open end 136 of cuff 134. The distal end 114 of tube 110 is telescopically fit into the proximal end 132 of mask portion 130, and LMA 100 provides a continuous, sealed, airway extending from proximal end 112 of tube 110 to the open end 136 of cuff 134. LMA 100 also includes an inflation tube 138 for selectively inflating or deflating cuff 134.
In operation, the cuff 134 is deflated, and then the mask portion is inserted through the patient's mouth into the patient's pharynx. The mask portion is preferably positioned so that a distal end 140 of cuff 134 rests against the patient's normally closed esophagus and so that the open end 136 of the cuff 134 is aligned with the entryway of the patient's trachea (i.e., the patient's glottic opening). After the mask portion is so positioned, the cuff is inflated thereby forming a seal around the patient's glottic opening and this establishes a sealed airway extending from the proximal end 112 of the tube 110 to the patient's trachea.
For convenience of exposition, the term “fully inserted configuration” shall be used herein to refer to an LMA that has been inserted into a patient and has the following characteristics: (1) the mask portion is disposed around the patient's glottic opening; (2) the cuff is inflated forming a seal around the patient's glottic opening; and (3) the airway tube extends from a proximal end located outside the patient's mouth to a distal end that is coupled to the mask portion, the tube extending through the patient's mouth and the patient's natural upper airway so that the LMA provides a sealed airway extending from the tube's proximal end to the patient's lungs. FIG. 2 shows an LMA in the fully inserted configuration.
When LMA 100 is in the fully inserted configuration, LMA 100 advantageously does not contact the interior lining of the trachea. Rather, the seal is established by contact between the tissues surrounding the patient's laryngeal inlet and the inflatable cuff 134. Unlike the delicate interior lining of the trachea, the tissues at the laryngeal inlet are accustomed to contact with foreign matter. For example, during the act of swallowing food, the food is normally squeezed against these tissues on its way to the esophagus. These tissues are accordingly less sensitive and less susceptible to being damaged by contact with the inflatable cuff.
FIG. 3 shows a sectional side view of the mask portion 230 of another prior art LMA. The illustrated mask portion 230, which is described more fully in U.S. Pat. No. 5,355,879, includes an inflatable cuff 234 and a backplate 250. Backplate 250 defines a proximal end 232 for receiving, or coupling to, a cylindrical airway tube (not shown). Mask portion 230 defines a sealed passageway, or airway, that extends from proximal end 232 through to the open end 236 of cuff 234. This mask portion 230 also includes an inflatable back cushion that, when inflated, expands to the contour illustrated by phantom outline 252. As shown in FIG. 3, the cross sections of prior art cuffs are generally circular. The thickness T1 of the material used to form the cuff (i.e., the thickness of the cuff wall) is normally about 0.7–0.8 millimeters.
U.S. Pat. No. 5,303,697 describes an example of another type of prior art LMA that is commonly known as an “intubating LMA”. The intubating LMA is useful for facilitating insertion of an endotracheal tube. After an intubating LMA has been located in the fully inserted configuration, the LMA can act as a guide for a subsequently inserted endotracheal tube. Use of the LMA in this fashion facilitates what is commonly known as “blind insertion” of the endotracheal tube. Only minor movements of the patient's head, neck, and jaw are required to insert the intubating LMA, and once the intubating LMA has been located in the fully inserted configuration, the endotracheal tube may be inserted with virtually no additional movements of the patient. This stands in contrast to the relatively large motions of the patient's head, neck, and jaw that would be required if the endotracheal tube were inserted without the assistance of the intubating LMA.
U.S. Pat. No. 5,632,271 describes an example of yet another type of prior art LMA. In addition to providing an airway tube for ventilating a patient's lungs, this LMA also provides a second tube, a drainage tube, used for draining or removing regurgitated material. The distal end of the drainage tube is disposed proximal to the normally closed entrance to the patient's esophagus. In addition to providing drainage, the drainage tube may also be used to guide insertion of a gastric tube.
In general, prior art LMAs have been manufactured by molding elastomeric materials such as silicone to desired shapes. One advantage of these materials is that they are durable enough to permit the LMAs to be sterilized in an autoclave and reused. For example, LMAs sold by LMA International SA of Henley, England are guaranteed to survive forty sterilizations, and in practice these devices may generally be sterilized (and reused) more than forty times before becoming too worn for reuse. However, one disadvantage of these materials is that they are relatively expensive. Accordingly, it would be advantageous to develop a reduced cost LMA.
Several attempts have been made in the prior art to provide reduced cost LMAs. For example, U.S. Pat. No. 6,012,452 discloses an LMA in which the mask portion is formed by adhering a foam material to both sides of a backplate. The foam forms an inflatable cuff that is attached to both sides of the plate. U.S. Pat. No. 5,983,897 discloses another LMA in which the mask portion is formed by attaching cuff members to the top and bottom of a backplate. The cuff members may be formed from flexible, resilient plastics material, such as PVC. One disadvantage of the LMAs disclosed in the '897 and '452 patents is that the assembly of the disclosed mask portions necessarily involves two steps: a first step of fabricating the backplate and then a second step of adhering the cuff to the top and bottom of the plate. It would therefore be advantageous to develop a process for simultaneously forming all parts of the mask portion of an LMA.
In addition to cost, another disadvantage of prior art LMAs relates to the quality of the seal established between the patient and the LMA. The LMA shown in FIG. 1 generally maintains a seal up to about twenty cm H2O. That is, when the LMA is in the fully inserted configuration, the seal between the LMA and the patient will be maintained as long as the pressure applied to the proximal end of the airway tube is less than approximately twenty cm H2O. However, if greater pressures are applied to the proximal end of the airway tube, the seal tends to be lost thereby causing loss of some fraction of the delivered gas volume, so that positive pressure ventilation may be less effective. This stands in contrast to the endotracheal tube, which can normally maintain a seal up to fifty cm H2O. Accordingly, it would be advantageous to provide an LMA that provides improved seals.
Still another disadvantage of prior art LMAs relates to the profile, or geometric configuration, of the deflated LMA. When the cuff of an LMA is deflated, the LMA would ideally, automatically, assume a shape that was optimized for facilitating insertion. However, prior art LMAs do not tend to automatically form such shapes when the cuff is deflated. Accordingly, several “forming tools” have been provided for affecting the shape of the deflated LMA. U.S. Pat. No. 5,711,293 discloses one such forming tool. However, it would be advantageous to provide an LMA that automatically assumed a profile that facilitated insertion when the cuff was deflated.
Yet another disadvantage of prior art LMAs relates to the manner in which they are inserted into a patient. Anesthesiologists or other practitioners insert many types of prior art LMAs by pushing one of their fingers against the proximal end of the cuff. Unfortunately, this procedure requires the practitioner to insert their finger into the patient's mouth and guide the LMA past the patient's throat. Since many practitioners prefer to avoid inserting their fingers into patient's mouths, several insertion tools have been developed for facilitating insertion of various LMAs. However, it would be advantageous to provide an LMA that could be inserted without an insertion tool and without requiring insertion of a finger into the patient's mouth.